205 research outputs found
Calculating the Fierz Transformation for Higher Orders
We consider the higher-order Fierz transformation, which corresponds to
expanding a product of terms into a sum of products of
Dirac densities and currents. It is shown that the Fierz transformation can be
obtained by solving a large system of linear equations with fractional complex
coefficients, which is practical at least up to fourth power.Comment: 6 pages, 3 table
On the Isovector Channels in Relativistic Point Coupling Models within the Hartree and Hartree-Fock Approximations
We investigate the consequences of Fierz transformations acting upon the
contact interactions for nucleon fields occurring in relativistic point
coupling models in Hartree approximation, which yield the same models but in
Hartree-Fock approximation instead. We find for four-fermion interactions
occurring in two existing relativistic point coupling phenomenologies that
whereas in Hartree the isovector-scalar strength, corresponding to delta-meson
exchange, is unnaturally small, indicating a possible new symmetry, in
Hartree-Fock it is instead comparable to the isovector-vector strength
corresponding to rho-meson exchange, but the sum of the two isovector coupling
constants appears to be preserved in both approaches. Furthermore, in
Hartree-Fock approximation, both QCD-scaled isovector coupling constants are
natural (dimensionless and of order 1) whereas in Hartree approximation only
that of the isovector-vector channel is natural. This indicates that it is not
necessary to search for a new symmetry and, moreover, that the role of the
delta-meson should be reexamined.Comment: 10 pages; accepted for publication in Nuclear Physics
Jockeying for position: the construction of masculine identities
In this paper we examine the construction of masculine identities within a real-life social situation. Using data from an extensive series of interviews with small groups of sixth-form (17-18-year-old) students attending a UK-based, single-sex independent school, the analysis looks at the action orientation of different constructions of identity. More specifically, it focuses upon how the identity talk of one particular group of students were oriented towards managing their subordinate status within the school. In a number of instances the identity of the `new man' was adopted as a strategy of resistance. However, it was found that the more common strategy involved buying back into values embodied within a more traditional definition of masculinity
Nuclear Ground State Observables and QCD Scaling in a Refined Relativistic Point Coupling Model
We present results obtained in the calculation of nuclear ground state
properties in relativistic Hartree approximation using a Lagrangian whose
QCD-scaled coupling constants are all natural (dimensionless and of order 1).
Our model consists of four-, six-, and eight-fermion point couplings (contact
interactions) together with derivative terms representing, respectively, two-,
three-, and four-body forces and the finite ranges of the corresponding mesonic
interactions. The coupling constants have been determined in a self-consistent
procedure that solves the model equations for representative nuclei
simultaneously in a generalized nonlinear least-squares adjustment algorithm.
The extracted coupling constants allow us to predict ground state properties of
a much larger set of even-even nuclei to good accuracy. The fact that the
extracted coupling constants are all natural leads to the conclusion that QCD
scaling and chiral symmetry apply to finite nuclei.Comment: 44 pages, 13 figures, 9 tables, REVTEX, accepted for publication in
Phys. Rev.
Search for Higgs Bosons in e+e- Collisions at 183 GeV
The data collected by the OPAL experiment at sqrts=183 GeV were used to
search for Higgs bosons which are predicted by the Standard Model and various
extensions, such as general models with two Higgs field doublets and the
Minimal Supersymmetric Standard Model (MSSM). The data correspond to an
integrated luminosity of approximately 54pb-1. None of the searches for neutral
and charged Higgs bosons have revealed an excess of events beyond the expected
background. This negative outcome, in combination with similar results from
searches at lower energies, leads to new limits for the Higgs boson masses and
other model parameters. In particular, the 95% confidence level lower limit for
the mass of the Standard Model Higgs boson is 88.3 GeV. Charged Higgs bosons
can be excluded for masses up to 59.5 GeV. In the MSSM, mh > 70.5 GeV and mA >
72.0 GeV are obtained for tan{beta}>1, no and maximal scalar top mixing and
soft SUSY-breaking masses of 1 TeV. The range 0.8 < tanb < 1.9 is excluded for
minimal scalar top mixing and m{top} < 175 GeV. More general scans of the MSSM
parameter space are also considered.Comment: 49 pages. LaTeX, including 33 eps figures, submitted to European
Physical Journal
A Measurement of the Product Branching Ratio f(b->Lambda_b).BR(Lambda_b->Lambda X) in Z0 Decays
The product branching ratio, f(b->Lambda_b).BR(Lambda_b->Lambda X), where
Lambda_b denotes any weakly-decaying b-baryon, has been measured using the OPAL
detector at LEP. Lambda_b are selected by the presence of energetic Lambda
particles in bottom events tagged by the presence of displaced secondary
vertices. A fit to the momenta of the Lambda particles separates signal from B
meson and fragmentation backgrounds. The measured product branching ratio is
f(b->Lambda_b).BR(Lambda_b->Lambda X) = (2.67+-0.38(stat)+0.67-0.60(sys))%
Combined with a previous OPAL measurement, one obtains
f(b->Lambda_b).BR(Lambda_b->Lambda X) = (3.50+-0.32(stat)+-0.35(sys))%.Comment: 16 pages, LaTeX, 3 eps figs included, submitted to the European
Physical Journal
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
Measurement of isolated photon production in pp and PbPb collisions at sqrt(sNN) = 2.76 TeV
Isolated photon production is measured in proton-proton and lead-lead
collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the
pseudorapidity range |eta|<1.44 and transverse energies ET between 20 and 80
GeV with the CMS detector at the LHC. The measured ET spectra are found to be
in good agreement with next-to-leading-order perturbative QCD predictions. The
ratio of PbPb to pp isolated photon ET-differential yields, scaled by the
number of incoherent nucleon-nucleon collisions, is consistent with unity for
all PbPb reaction centralities.Comment: Submitted to Physics Letters
The effect of patient observation on cranial computed tomography rates in children with minor head trauma
BackgroundManagement of children with minor blunt head trauma often includes a period of observation to determine the need for cranial computed tomography (CT). Our objective was to estimate the effect of planned observation on CT use for each Pediatric Emergency Care Applied Research Network (PECARN) traumatic brain injury (TBI) risk group among children with minor head trauma.MethodsThis was a secondary analysis of a prospective observational study at 10 emergency departments (EDs) in Australia and New Zealand, including 18,471 children 24 hours for head trauma, or hospitalization for â„ 2 nights in association with a positive cranial CT scan. We estimated the odds of cranial CT use with planned observation, adjusting for patient characteristics, PECARN TBI risk group, history of seizure, time from injury, and hospital clustering, using a generalized linear model with mixed effects.ResultsThe cranial CT rate in the total cohort was 8.6%, and 0.8% had ciTBI. The planned observation group had 4,945 (27%) children compared to 13,526 (73%) in the no planned observation group. Cranial CT use was significantly lower with planned observation (adjusted odds ratio [OR] = 0.2, 95% confidence interval [CI] = 0.1 to 0.1), with no difference in missed ciTBI rates. There was no difference in the odds of cranial CT use with planned observation for the group at very low risk for ciTBI (adjusted OR = 0.9, 95% CI = 0.5 to 1.4). Planned observation was associated with significantly lower cranial CT use in patients at intermediate risk (adjusted OR = 0.2, 95% CI = 0.2 to 0.3) and high risk (adjusted OR = 0.1, 95% CI = 0.0 to 0.1) for ciTBI.ConclusionsEven in a setting with low overall cranial CT rates in children with minor head trauma, planned observation was associated with decreased cranial CT use. This strategy can be safely implemented on selected patients in the PECARN intermediateâ and higherârisk groups for ciTBI
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